The present invention relates to a laser reference level setting device for setting a reference line in various types of civil engineering works.
In case of civil engineering works, it is necessary to have a horizontal reference line or a reference line tilted at a predetermined angle with respect to the horizontal line. A laser reference level setting device is used to set this reference line.
In case concrete pipes are buried in sewage construction, the pipes must be laid without bending and also must be tilted at a predetermined angle.
The concrete pipe of this type is used as a flow passage for city water, sewage water, and other liquid, and it is laid with a certain gradient and without bending. If the buried concrete pipes meander in horizontal or vertical directions, the water or other liquid stagnates or is stopped or leaked into soil, and the pipes no more fulfill the role as a flow passage. Therefore, to install the concrete pipes in a proper manner, it is necessary to have an adequate reference line.
As the reference line of this type, a laser beam is the most suitable because it does not slack like a thread even when it is used for a long distance, does not hinder installation and other operation, or is not cut off due to interference with the concrete pipe during the construction work. The laser reference level setting device as described above is used to form the reference line by projecting a laser beam when the concrete pipes are installed.
As a typical technique to bury concrete pipes underground, an open cut technique is known. In this technique, the ground is dug, and concrete pipes are laid and buried one after another in the ditch and are covered with soil.
In the following, description will be given on the open cut technique referring to FIG. 8.
The laser reference level setting device comprises a laser irradiation unit 1 for projecting a laser beam in the horizontal direction or in a direction with a gradient, and a target 9. When the laser beam projected from the laser irradiation unit 1 is aligned with the horizontal line, a horizontal reference line is formed. When the laser beam is tilted at a predetermined angle, a reference line with a gradient is formed.
At regular interval along a linear section, a vertical pit 3 is excavated with a depth, which is deeper than the depth to install concrete pipes at each starting point to bury concrete pipes 2, and a burial ditch 4 continuous to the vertical pit 3 is dug to a depth deeper than the depth to bury the concrete pipes. The laser irradiation unit 1 is installed in the vertical pit 3, and a laser beam is projected at a gradient of .theta., and a reference laser beam L is formed. The concrete pipes 2 are laid in the burial ditch 4 via a provisional base 5 so that the axis of the concrete pipes 2 is aligned with the reference laser beam L. When the axis of the concrete pipes 2 is aligned with the reference laser beam L, the burial ditch 4 is filled with soil, and the concrete pipes 2 are buried.
In the laser irradiation unit 1, its position in the horizontal direction must be accurately set. For the accurate positioning of the laser irradiation unit 1 in the horizontal direction, a support stand 6 is installed above the vertical pit 3, and a transit 7 is placed on the support stand 6. A plumb-bob is suspended from the transit 7, and a known point is set. Further, the laser irradiation unit 1 is installed in the vertical pit 3, and the plumb-bob is aligned with the center of the laser irradiation unit 1. Then, the plumb-bob is suspended from the laser irradiation unit 1, and the plumb-bob is aligned with the known point.
In the open cut method, the concrete pipe 2 is provisionally installed at a terminal end of the burial ditch 4, and a target 9 is placed in it. The distance from the center of the target to a point of the target touching the ground is equal to the inner radius of the concrete pipe 2. As a result, when the target is placed in the concrete pipe 2, the center of the target is aligned with the center of the concrete pipe 2.
A portion of the target 9 where a laser beam is projected i.e. a target plate, is made of semi-transparent material. Thus, it is possible to confirm a projecting position of the laser beam and the transmitted laser beam is diffused in conical form, and a projected position of the target 9 can be confirmed within the range of diffusion of the transmitted laser beam. To set tilting of the laser beam projected from the laser irradiation unit 1, a tilt setting angle is inputted to the laser irradiation unit 1. A tilting mechanism is incorporated in the laser irradiation unit 1. The tilting mechanism is operated to set the laser beam at a predetermined tilt angle.
The target 9 is at a position on the extension of the laser beam projected from the laser irradiation unit 1, and the projecting position of the laser beam is confirmed. In case the projected laser beam is deviated from the center of the target 9, the provisionally installed concrete pipe 2 or the laser beam is adjusted in the vertical direction for vertical adjustment. For the deviation in the lateral direction, a regulating device (not shown) of main unit of the system is manually operated or the concrete pipe is adjusted, so that the laser beam is aligned with the center of the target 9 while confirming the laser beam projecting position of the target 9 from the direction of the laser irradiation unit 1. The concrete pipes 2 are installed using the laser beam projected to the center of the target 9 as a reference line.
There are several methods to control the laser beam projected from the laser reference level setting device: to flash on and off the projecting laser beam, to perform auto alignment, i.e. to automatically project in the horizontal direction and align the laser beam with the center of the target, or to perform tilt setting, i.e. to tilt the direction of the laser beam. The control operations as described above can be performed from an operation panel provided on the laser reference level setting device. To facilitate the operation, remote control system is adopted. The projected light is visible light, but it is the laser beam with high directivity. It is difficult to visually confirm unless it is projected to an object with high diffusivity. It is difficult to visually confirm even at nighttime when there is rather high contrast from the surrounding. In daytime, it is much more difficult because of sunlight. Even when it is tried to set the direction of the projected laser beam by remote control operation, the operation cannot be confirmed until the result is known. For example, in case the laser reference level setting device is installed at a reference point and the laser beam is directed toward a target placed at a predetermined position in the first stage of the setting operation, it is difficult to confirm whether remote control operation is being achieved or not during the setting operation because a laser beam has high directivity and operation cannot be visually confirmed until the laser beam is projected and diffused.